1. Field of the Invention
This invention relates to photography and, more particularly, to an anti-flare structure for use in a photographic optical system.
2. Description of the Prior Art
In photographic optical systems the objective lens will generally satisfactorily reproduce a larger conjugate object area than is desired to be recorded in the photographic emulsion. Consequently, radiation from outside of the desired field of view of the system can enter the system through the objective lens because the lens "sees" more than is necessary. Once this unwanted radiation enters the system, it can reflect off the system's internal support structure, e.g., camera walls, and eventually reach the photographic emulsion. When this occurs, depending on the nature of the internal reflections, either extraneous images are recorded in the emulsion or an overall fog results causing a reduction in the contrast of the final picture. In either case, the quality of the final picture is seriously degraded if the unwanted radiation is not prevented from reaching the emulsion during exposure.
There are fundamentally two ways of dealing with this problem. The first way is to prevent the unwanted radiation from entering the objective lens by making its field correspond to the field of view of the system. The second is to allow the unwanted radiation to enter the system and then prevent it from reaching the emulsion by absorbing it in the system or by providing an internal baffling arrangement which prevents the emulsion from seeing it. An example of the first is described in U.S. Pat. No. 3,488,103 issued Jan. 6, 1970, and entitled "Anti-Glare Improvement For Optical Imaging Systems". In this patent an external anti-glare baffle having a specularly reflective surface formed from an oblate hemispheroid is described. An aperture in an upper horizontal surface of the hemispheroid is defined by all the foci of the hemispheroid such that rays which enter the baffle through the aperture or through the foci at the edges of the aperture and impinge on the reflective surface are specularly reflected out of the baffle. A viewing aperture is provided at the centeral portion of the reflective surface for permitting passage of rays emanating from within the desired field of view. Although this arrangement is effective, it would be impractical to use it with a photographic system where size is a limitation. The more conventional solution, especially in photographic systems, e.g. cameras, is to use the second way. Included in the second category are such solutions as lining the interior of the systems with an absorbing material such as flocking, spraying the interior with a highly non-reflective flat black coating of paint, or providing a baffling arrangement. These solutions, too, are satisfactory but have limitations where the size and manufacture of the optical system are overriding concerns. For example, adding flocking material or painting are secondary manufacturing operations. Internal baffling arrangements add size as well as additional manufacturing steps, but can be quite effective, as, for example, their application in Polaroid Corporation's Square Shooter 2 Land Cameras where they are used in combination with specularly reflective light traps running perpendicular to the optical axis of the camera. Therefore, a solution is required which will permit the simplified manufacture of a minimum sized photographic optical system that will effectively deal with unwanted radiation outside its field of view.